Phosphorus containing bis(tridenate) osmium complexes

ABSTRACT

Bis(tridentate) osmium(II) complexes containing phosphite groups useful as phosphorescent emitters are disclosed. The disclosed osmium(II) complexes have higher oxidation potential then previously known osmium(II) complexes. An organic light emitting device having an organic layer that includes the disclosed osmium(II) complex is also disclosed.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to compounds for use as emitters anddevices, such as organic light emitting diodes, including the same. Moreparticularly, the compounds disclosed herein are novel phosphoruscontaining bis(tridentate) osmium complexes.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY

According to an embodiment, a compound is provided that comprises astructure selected from the group consisting of:

wherein

each independently represents a tridentate ligand coordinating to osmiumthrough coordinating atoms of X, carbon and phosphorus; and wherein X isselected from the group consisting of nitrogen, oxygen, sulfur, andcarbon.

According to another aspect of the present disclosure, a first devicecomprising a first organic light emitting device is provided. The firstorganic light emitting device can comprise an anode, a cathode, and anorganic layer, disposed between the anode and the cathode. The organiclayer can include a compound comprising a structure selected from thegroup consisting of Formula I and Formula II. The first device can be aconsumer product, an organic light-emitting device, and/or a lightingpanel.

The compounds disclosed herein are novel ancillary ligands for metalcomplexes. The incorporation of these ligands can narrow the emissionspectrum, decrease evaporation temperature, and improve deviceefficiency. The inventors have discovered that incorporating these novelancillary ligands in iridium complexes improved sublimation of theresulting iridium complexes, color spectrum of phosphorescence by theseiridium complexes, and their EQE.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows Formulas I and II as disclosed herein.

FIG. 4 shows the molecular structure of the inventive Compound 1.

FIG. 5 is a graph showing a correlation between calculated HOMO leveland oxidation potential (measured by cyclic voltammetry).

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink jet and OVJD. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processability than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, medical monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, heads up displays, fully transparent displays, flexibledisplays, laser printers, telephones, cell phones, personal digitalassistants (PDAs), laptop computers, digital cameras, camcorders,viewfinders, micro-displays, 3-D displays, vehicles, a large area wall,theater or stadium screen, or a sign. Various control mechanisms may beused to control devices fabricated in accordance with the presentinvention, including passive matrix and active matrix. Many of thedevices are intended for use in a temperature range comfortable tohumans, such as 18 degrees C. to 30 degrees C., and more preferably atroom temperature (20-25 degrees C.), but could be used outside thistemperature range, for example, from −40 degree C. to +80 degree C.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

As used herein, “substituted” indicates that a substituent other than His bonded to the relevant carbon. Thus, where R² is monosubstituted,then one R² must be other than H. Similarly, where R³ is disubstituted,then two of R³ must be other than H. Similarly, where R² isunsubstituted R² is hydrogen for all available positions.

According to an embodiment, novel phosphorus containing bis(tridentate)osmium complexes are disclosed. The inventors have discovered that thesenovel compounds are useful as emitters in phosphorescent OLEDs.

Osmium (II) complexes have been investigated for OLED applications. (SeeEur. J. Inorg. Chem. 2006, 3319-3332). The octahedral ligand arrangementof the Os(II) complexes resembles that of Ir(III) complexes. Os(II)complexes generally exhibit low oxidation potential, i.e. shallow HOMOenergy level, than IR(III) complexes. Generally, the low oxidationpotential make OS(II) complexes not compatible with the mainstreammatrix materials in OLED devices. The low oxidation potential alsopresents difficulty in tuning the phosphorescence to the blue colorregime.

In the present disclosure, however, the inventors disclose novelosmium(II) complexes in which the above-mentioned problems have beensolved by utilizing the high electron withdrawing property of phosphite.By incorporating phosphite groups in the molecule, the inventors haveproduced osmium(II) complexes with much deeper oxidation potential.

According to an embodiment, a compound is provided that comprises astructure selected from the group consisting of:

wherein

each independently represents a tridentate ligand coordinating to osmiumthrough coordinating atoms of X, carbon and phosphorus; and wherein X isselected from the group consisting of nitrogen, oxygen, sulfur, andcarbon.

According to other embodiments of the compound, X is a neutral donoratom, C is an anionic donor carbon, and P is a neutral donor phosphorus.The compound can be neutral.

In one embodiment, X is a carbon, and Os—X bond is a metal-carbene bond.In another embodiment, the compound is homoleptic. In anotherembodiment, the compound is heteroleptic.

In another, the compound has the structure of

In another embodiment, the compound has the structure of

wherein each of R¹ and R² is phenol or phenyl;wherein Y comprises carbon or oxygen;wherein ring A comprises a heterocyclic ring comprising pyridine,imidazole, pyrazole, NHC carbene, or quinoline;wherein R³ is alkyl;wherein R³ can represent mono-, di-, or tri-substitutions, or nosubstitution; andwherein any two adjacent substituents of R¹, R², and R³ are optionallyjoined to form a ring.

In another embodiment, the compound is selected from the groupconsisting of

According to another aspect of the present disclosure, a first devicecomprising a first organic light emitting device is disclosed. The firstorganic light emitting device comprises an anode; a cathode; and anorganic layer, disposed between the anode and the cathode, comprising acompound having a structure selected from the group consisting of:

wherein

each independently represents a tridentate ligand coordinating to osmiumthrough coordinating atoms of X, carbon and phosphorus; and wherein X isselected from the group consisting of nitrogen, oxygen, sulfur, andcarbon.

In an embodiment of the first device, X is a neutral donor atom, C is ananionic donor carbon, and P is a neutral donor phosphorus. In anotherembodiment of the first device, the compound has the structure of

wherein R¹ and R² is phenol or phenyl;wherein Y comprises carbon or oxygen;wherein ring A comprises a heterocyclic ring comprising pyridine,imidazole, pyrazole, NHC carbene, or quninoline;wherein R³ is alkyl;wherein R³ can represent mono-, di-, or tri-substitutions, or nosubstitution; andwherein any two adjacent substituents of R¹, R², and R³ are optionallyjoined to form a ring.

The first device can be a consumer product. The first device can be anorganic light emitting device. The first device can comprise a lightpanel.

In another embodiment of the first device, the organic layer is anemissive layer and the compound is an emissive dopant. In anotherembodiment, the compound is a non-emissive dopant in the emissive layer.

In another embodiment of the first device, the organic layer furthercomprises a host material. The host material can comprise a triphenylenecontaining benzo-fused thiophene or benzo-fused furan; wherein anysubstituent in the host material is an unfused substituent independentlyselected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1),OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1),C≡C—C_(n)H_(2n+1), Ar₁, Ar₁-Ar₂, C_(n)H_(2n)—Ar₁, or no substitution;

wherein n is from 1 to 10; and

wherein Ar₁ and Ar₂ are independently selected from the group consistingof benzene, biphenyl, naphthalene, triphenylene, carbazole, andheteroaromatic analogs thereof.

In another embodiment, the host material comprises at least one chemicalgroup selected from the group consisting of carbazole, dibenzothiphene,dibenzofuran, dibenzoselenophene, azacarbazole, aza-dibenzothiophene,aza-dibenzofuran, and aza-dibenzoselenophene.

In another embodiment, the host material is selected from the groupconsisting of

and combinations thereof.

In yet another embodiment, the host material comprises a metal complex.

According to another aspect of the present disclosure, a novelformulation is disclosed. The formulation comprises a compound having astructure selected from the group consisting of:

wherein

each independently represents a tridentate ligand coordinating to osmiumthrough coordinating atoms of X, carbon and phosphorus; and wherein X isselected from the group consisting of nitrogen, oxygen, sulfur, andcarbon.Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but not limit to: aphthalocyanine or porphryin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and silane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, azulene; group consisting aromaticheterocyclic compounds such as dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine; and groupconsisting 2 to 10 cyclic structural units which are groups of the sametype or different types selected from the aromatic hydrocarbon cyclicgroup and the aromatic heterocyclic group and are bonded to each otherdirectly or via at least one of oxygen atom, nitrogen atom, sulfur atom,silicon atom, phosphorus atom, boron atom, chain structural unit and thealiphatic cyclic group. Wherein each Ar is further substituted by asubstituent selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH)or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but not limit tothe following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40;(Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independentlyselected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and k′+k″ is the maximum number of ligands thatmay be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative. In anotheraspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met isselected from Ir, Pt, Os, and Zn. In a further aspect, the metal complexhas a smallest oxidation potential in solution vs. Fc⁺/Fc couple lessthan about 0.6 V.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. While the Table below categorizes host materials as preferredfor devices that emit various colors, any host material may be used withany dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴are independently selected from C, N, O, P, and S; L¹⁰¹ is an anotherligand; k′ is an integer value from 1 to the maximum number of ligandsthat may be attached to the metal; and k′+k″ is the maximum number ofligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms Oand N.

In another aspect, Met is selected from Ir and Pt. In a further aspect,(Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the groupconsisting aromatic hydrocarbon cyclic compounds such as benzene,biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene,phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; groupconsisting aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and group consisting 2 to 10 cyclic structural units which are groups ofthe same type or different types selected from the aromatic hydrocarboncyclic group and the aromatic heterocyclic group and are bonded to eachother directly or via at least one of oxygen atom, nitrogen atome,sulfur atom, silicon atom, phosphorus atom, boron atom, chain structuralunit and the aliphatic cyclic group. Wherein each group is furthersubstituted by a substituent selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.

In one aspect, host compound contains at least one of the followinggroups in the molecule:

wherein R¹⁰¹ to R¹⁰⁷ is independently selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof, when it is aryl or heteroaryl, ithas the similar definition as Ar's mentioned above. k is an integer from0 to 20 or 1 to 20; k′″ is an integer from 0 to 20. X¹⁰¹ to X¹⁰⁸ isselected from C (including CH) or N. Z¹⁰¹ and Z¹⁰² is selected fromNR¹⁰¹, O, or S.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

In one aspect, compound used in HBL contains the same molecule or thesame functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ isan integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy,aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl,aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof, when it is aryl or heteroaryl, it has the similar definition asAr's mentioned above. Ar¹ to Ar^(a) has the similar definition as Ar'smentioned above. k is an integer from 1 to 20. X¹⁰¹ to X¹⁰⁸ is selectedfrom C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinatedto atoms O, N or N, N; L¹⁰¹ is another ligand; k′ is an integer valuefrom 1 to the maximum number of ligands that may be attached to themetal.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated. Thus, anyspecifically listed substituent, such as, without limitation, methyl,phenyl, pyridyl, etc. encompasses undeuterated, partially deuterated,and fully deuterated versions thereof. Similarly, classes ofsubstituents such as, without limitation, alkyl, aryl, cycloalkyl,heteroaryl, etc. also encompass undeuterated, partially deuterated, andfully deuterated versions thereof.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 2below. Table 2 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

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EXPERIMENTAL Material Synthesis

All reactions were carried out under nitrogen protections unlessspecified otherwise. All solvents for reactions are anhydrous and usedas received from commercial sources.

Synthesis of Compound 1

Synthesis of2-(3-((dichlorophosphino)oxy)phenyl)-1-(2,6-diisopropylphenyl)-1H-imidazole

A 100 mL round-bottomed flask was charged with3-(1-(2,6-diisopropylphenyl)-1H-imidazol-2-yl)phenol (0.309 g, 0.964mmol), trichlorophosphine (0.3 ml, 3.44 mmol) and 30 ml ofdichloromethane. A solution of triethylamine (0.135 ml, 0.964 mmol) in60 ml of dichloromethane was added dropwise at −20° C. for a period of 1hr. The reaction mixture was then stirred for 16 hrs. The reactionmixture was used for the next step without purification.

Synthesis of 3-(1-(2,6-diisopropylphenyl)-1H-imidazol-2-yl)phenylbis(2,6-dimethylphenyl)phosphite

A solution of 2,6-dimethylphenol (1.413 g, 11.56 mmol), triethylamine(1.614 ml, 11.56 mmol) and dichloromethane (20 ml) was added dropwise tothe reaction mixture from the previous step at 0° C. The reactionmixture was then stirred at room temperature for 2.5 hrs. The reactionmixture was then filtered and the filtrate was subjected to columnchromatography (SiO₂, 100% DCM to 20% ETOAC in DCM) to yield the desiredproduct, 3-(1-(2,6-diisopropylphenyl)-1H-imidazol-2-yl)phenylbis(2,6-dimethylphenyl)phosphite. (0.338 g, 59%).

Synthesis of OsH₄(PPh₃)₃

A 500 mL round-bottomed flask was charged with triphenylphosphine (15.74g, 60.0 mmol) and ethanol (Volume: 400 ml) to give a colorless solution.The reaction mixture was heated to reflux, then (NH₄)₂OsCl₆(4.39 g,10.00 mmol) was added in one portion. A solution of NaBH₄ (2.001 g, 52.9mmol) in 300 ml of ethanol was added dropwise to the reaction mixturefor a period of 10 mins. The reaction mixture was heated to reflux foranother 15 mins. The reaction mixture was then cooled down. The solidwas filtered and washed in sequence with ethanol, water, ethanol, andhexane to yield the desired product, OsH₄(PPh₃)₃. (8.32 g, 85%).

Synthesis of Compound 1:

A 100 mL round-bottomed flask was charged with3-(1-(2,6-diisopropylphenyl)-1H-imidazol-2-yl)phenylbis(2,6-dimethylphenyl)phosphite (0.334 g, 0.564 mmol),OsH₄(PPh₃)₃(0.240 g, 0.245 mmol) in decahydronaphthalene (Volume: 5 ml)to give a white suspension. The reaction mixture was heated to 200° C.for 1.5 hr. The solvent was removed by vacuum distillation and theresidue was subjected to column chromatography (SiO₂, 15% etoac to 20%etoac in heptane) to yield Compound 1. (0.178 g, 53%).

Synthesis of Compound 2

Synthesis of1-([1,1′:3′,1″-terphenyl]-2′-yl)-2-(3-((diphenylphosphino)oxy)-5-methylphenyl)-1H-imidazole

A 250 mL round-bottomed flask was charged with3-(1-([1,1′:3′,1″-terphenyl]-2′-yl)-1H-imidazol-2-yl)-5-methylphenol(0.406 g, 1.009 mmol), chlorodiphenylphosphine (0.186 ml, 1.009 mmol),triethylamine (0.672 ml, 4.81 mmol) and toluene (Volume: 70 ml) to givea brown solution. The reaction mixture was heated to 90° C. for 16 hrs.The reaction mixture was filtered and the filtrate was subjected tocolumn chromatography (SiO2, 35% etoac to 50% etoac in heptane) to yieldthe desired product,1-([1,1′:3′,1″-terphenyl]-2′-yl)-2-(3-((diphenylphosphino)oxy)-5-methylphenyl)-1H-imidazole.(0.395 g, 66%).

Synthesis of Compound 2:

A 100 mL round-bottomed flask was charged with1-([1,1′:3′,1″-terphenyl]-2′-yl)-2-(3-((diphenylphosphino)oxy)-5-methylphenyl)-1H-imidazole(0.388 g, 0.66 mmol), OsH₄(PPh₃)₃(0.28 g, 0.288 mmol) anddecahydronaphthalene (Volume: 6 ml) to give a white suspension. Thereaction mixture was heated to 200° C. for 1.5 hr. The solvent wasremoved by vacuum distillation and the residue was subjected to columnchromatography (SiO₂, 15% etoac to 20% etoac in heptane) to yieldCompound 2. (0.34 g, 89%).

Synthesis of Compound 3

Synthesis of 2-((dichlorophosphino)oxy)-6-phenylpyridine

A 100 mL round-bottomed flask was charged with 6-phenylpyridin-2-ol(0.814 g, 4.75 mmol), trichlorophosphine (1.245 ml, 14.26 mmol) andCH₂Cl₂ (Volume: 120 ml) to give a white suspension. A solution oftriethylamine (0.664 ml, 4.75 mmol) in 60 ml of dichloromethane wasadded dropwise at −20° C. for a period of 1 hr. The reaction mixture wasthen stirred for 16 hrs. The reaction mixture was used for next stepwithout purification.

Synthesis of bis(2,6-dimethylphenyl) (6-phenylpyridin-2-yl)phosphite

A solution of 2,6-dimethylphenol (8.13 g, 66.6 mmol), triethylamine(9.29 ml, 66.6 mmol) and dichloromethane (20 ml) was added dropwise tothe reaction mixture from the previous step at 0° C. The reactionmixture was then stirred at room temperature for 2.5 hrs. The reactionmixture was then filtered and the filtrate was subjected to columnchromatography (SiO₂, 3% etoac in heptane to 5% etoac in heptane) toyield the desired product, bis(2,6-dimethylphenyl)(6-phenylpyridin-2-yl)phosphite. (1.17 g, 55%).

Synthesis of Compound 3:

A 100 mL round-bottomed flask was charged with (0.388 g, 0.66 mmol)bis(2,6-dimethylphenyl) (6-phenylpyridin-2-yl)phosphite,OsH₄(PPh₃)₃(1.939 g, 1.976 mmol) and decahydronaphthalene (Volume: 40ml) to give a white suspension. The reaction mixture was heated to 200°C. for 1.5 hrs. The solvent was removed by vacuum distillation andresidue was subjected to column chromatography (SiO₂, 10% etoac inheptane) to yield Compound 3. (0.95 g, 45%).

Device Test Data Device Examples

All example devices were fabricated by high vacuum (<10⁻⁷ Torr) thermalevaporation. The anode electrode consisted of 1200 Å of indium tin oxide(ITO). The cathode consisted of 10 Å of LiF followed by 1,000 Å of Al.All devices were encapsulated with a glass lid sealed with an epoxyresin in a nitrogen glove box (<1 ppm of H₂O and O₂) immediately afterfabrication, and a moisture getter was incorporated inside the package.

The organic stack of the device examples consisted of sequentially, fromthe ITO surface, 100 Å of LG101 (purchased from LG Chemical) as the holeinjection layer (HIL), 400 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (alpha-NPD) as the holetransporting layer (HTL), 300 Å of the invention compound, Compound 3,doped in Compound A as host with 15 weight percent of an osmiumphosphorescent compound as the emissive layer (EML), a 50 Å of CompoundA as electron blocking layer (EBL), 300 Å of LG201 (purchased from LGChemical) as the electron transporting layer (ETL). The resulting devicedata from those device examples is summarized in Table 2 below. As usedherein, NPD and Compound A have the following structures:

TABLE 2 Device Data λ_(max) FWHM Voltage LE EQE PE x y (nm) (nm) (V)(Cd/A) (%) (lm/W) Inventive 0.397 0.568 548 92 6.7 19.4 5.8 9.1 Example1 Compound 3

In the novel compound disclosed herein, the electron withdrawing abilityof phosphine/phosphite is used to lower the HOMO of osmium complexes tobe more comparable to iridium based dopants. The oxidation potentialvalues of the compounds provided in Table 3 below demonstrates thispoint.

TABLE 3 Oxidation potentials and the calculated HOMO level of thebis(tridenate) osmium complexes Experimental HOMO level OxidationStructure by calculation* potential** Example 1 (from US 2005/0260449)

−4.32 V −0.5 V Example 2 (from WO 2009046266)

−4.63 V −0.35 V Compound 1

−5.04 V 0.12 V Compound 3

−5.36 V 0.3 V Example 3

−3.44 V −1.2 V*** Example 4

−4.52 V −0.4 V*** *DFT (density function theory) calculation usingGaussian/B3lyp/cep-31g **Oxidation potential was referred to the anodicand cathodic peak potentials referenced to the Fc⁺/Fc couple in V.***extrapolated oxidation potential from Graph 1 shown in FIG. 5.Graph 1 shows a correlation between calculated HOMO level and oxidationpotential (measured by cyclic voltammetry).

Osmium (II) complexes have been investigated for OLED applications. (seereview: Eur. J. Inorg. Chem. 2006, 3319-3332). The octahedral ligandarrangement of the Os(II) complexes resembles that of Ir(III) complexes.Os(II) complexes generally exhibit low oxidation potential, i.e. shallowHOMO energy level than Ir(III) complexes. For example, the Examples 1and 2 in US 2005026049 and WO 2009046266, respectively, show oxidationpotential of −0.5V and −0.35V; in contrast with the oxidation potentialof 0.3V of Ir(PPY)3. The extremely shallow HOMO level of Osmiumbis(tridenate) complexes make it difficult to fit in the main streamoled device structure. According to the invention disclosed in thepresent disclosure, by taking advantage of the electron withdrawingability of the phosphine/phosphite; the inventors firmed Osmiumbis(tridenate) complexes having more reasonable HOMO levels. i.e.oxidation potential between 0 to 0.3V. For example, comparing Example 3and Compound 1; the oxidation potential changed from −1.2V to 0.12V byreplacing imidazole ring with phosphite group. Similarly, comparingExample 4 and Compound 3, the oxidation potential changed from −0.4V to0.3V by replacing a pyridine ring with a phosphite group. Moreover,phosphine moiety is part of tridenate frame. The rigid nature of thetridentate ligands generally results in narrow emission line widths andshort excited state lifetimes, which can result in better color purityand longer device lifetime, making them suitable for displayapplications.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

We claim:
 1. A compound having a structure selected from the group consisting of:

wherein

each independently represents a tridentate ligand coordinating to osmium through coordinating atoms of X, carbon and phosphorus; and wherein X is selected from the group consisting of nitrogen, oxygen, sulfur, and carbon.
 2. The compound of claim 1, wherein X is a neutral donor atom, C is an anionic donor carbon, and P is a neutral donor phosphorus.
 3. The compound of claim 1, wherein the compound is neutral.
 4. The compound of claim 1, wherein X is a carbon, and Os—X bond is a metal-carbene bond.
 5. The compound of claim 1, wherein the compound is homoleptic.
 6. The compound of claim 1, wherein the compound is heteroleptic.
 7. The compound of claim 1, wherein the compound has the structure of


8. The compound of claim 1, wherein the compound has the structure of

wherein each of R¹ and R² is phenol or phenyl; wherein Y comprises carbon or oxygen; wherein ring A comprises a heterocyclic ring comprising pyridine, imidazole, pyrazole, NHC carbene, or quninoline; wherein R³ is alkyl; wherein R³ can represent mono-, di-, or tri-substitutions, or no substitution; and wherein any two adjacent substituents of R¹, R², and R³ are optionally joined to form a ring.
 9. The compound of claim 1, wherein the compound is selected from the group consisting of


10. A first device comprising a first organic light emitting device, the first organic light emitting device comprising: an anode; a cathode; and an organic layer, disposed between the anode and the cathode, comprising a compound having a structure selected from the group consisting of:

wherein

each independently represents a tridentate ligand coordinating to osmium through coordinating atoms of X, carbon and phosphorus; and wherein X is selected from the group consisting of nitrogen, oxygen, sulfur, and carbon.
 11. The first device of claim 10, wherein X is a neutral donor atom, C is an anionic donor carbon, and P is a neutral donor phosphorus.
 12. The first device of claim 10, wherein the compound has the structure of

wherein R¹ and R² is phenol or phenyl; wherein Y comprises carbon or oxygen; wherein ring A comprises a heterocyclic ring comprising pyridine, imidazole, pyrazole, NHC carbene, or quninoline; wherein R³ is alkyl; wherein R³ can represent mono-, di-, or tri-substitutions, or no substitution; and wherein any two adjacent substituents of R¹, R², and R³ are optionally joined to form a ring.
 13. The first device of claim 10, wherein the first device is a consumer product.
 14. The first device of claim 10, wherein the first device is an organic light emitting device.
 15. The first device of claim 10, wherein the first device comprises a light panel.
 16. The first device of claim 10, wherein the organic layer is an emissive layer and the compound is an emissive dopant.
 17. The first device of claim 10, wherein the organic layer is an emissive layer and the compound is a non-emissive dopant.
 18. The first device of claim 10, wherein the organic layer further comprises a host material.
 19. The first device of claim 18, wherein the host material comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan; wherein any substituent in the host material is an unfused substituent independently selected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C≡C—C_(n)H_(2n+1), Ar₁, Ar₁-Ar₂, C_(n)H_(2n)—Ar₁, or no substitution; wherein n is from 1 to 10; and wherein Ar₁ and Ar₂ are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof.
 20. The first device of claim 18, wherein the host material comprises at least one chemical group selected from the group consisting of carbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene.
 21. The first device of claim 18, wherein the host material is selected from the group consisting of:

and combinations thereof.
 23. The first device of claim 18, wherein the host material comprises a metal complex.
 24. A formulation comprising a compound having a structure selected from the group consisting of:

wherein

each independently represents a tridentate ligand coordinating to osmium through coordinating atoms of X, carbon and phosphorus; and wherein X is selected from the group consisting of nitrogen, oxygen, sulfur, and carbon. 